1. Field of the Invention
The present invention relates to a speaker.
2. Description of the Related Art
Speakers are widely used not only in home audio equipment or a car audio system but also in various electronic devices, such as a personal computer, a mobile phone, a video game machine and the like. Such electronic devices are increasingly downsized, which calls on the speakers to be further downsized (lower profile) and provide enhanced performance, specifically to withstand higher power input as well as produce improved sound quality.
Due to the limited installation space allocated for a speaker in an electronic device, the speaker is forced to have an elongated geometry and at the same time required to withstand high power input. Such a speaker with an elongated shape has a limited minor axis dimension and is therefore prohibited from having a voice coil with a sufficiently large diameter thus being disadvantageous in terms of withstanding power input. If the diameter of the voice coil is increased without changing the minor axis dimension of the speaker, the width of a surround is forced to decrease accordingly, and therefore the amplitude of a diaphragm is limited, which results in preventing the speaker from withstanding high power input. Also, if the width of the surround is decreased, the lowest resonance frequency is increased, and the reproductive performance in the lower frequency is deteriorated.
FIG. 20 shows a cross section of a conventional elongated speaker 201, wherein the cross section of the speaker 201 taken along the minor axis direction is shown in the left side and the cross section thereof taken along the major axis direction is shown in the right side. The speaker 201 shown in FIG. 20 includes: a frame 202; a magnetic circuit 203 connected to the frame 202; a voice coil 204 suspended in a magnetic gap of the magnetic circuit 203; a surround 205 whose outer circumferential portion is connected to the frame 202; a diaphragm 206 which has its outer circumferential portion connected via the surround 205 to the frame 202 and which vibrates back and forth (vertically in the figure) together with the voice coil 204; a spider 207 which has its inner circumferential portion connected to the voice coil 204 and has its outer circumferential portion connected to the frame 202; and a center cap 208 to cover the front side (upper side in the figure) of the voice coil 204.
In the speaker 201 of FIG. 20, if the diameter of the voice coil 204 is increased in order to withstand high power input, the width of the surround 205 is further decreased thus increasing the lowest resonance frequency, and the reproductive performance in the lower frequency is deteriorated. In order to overcome the problem described above, a solution is proposed in Japanese Patent No. 3956485.
FIG. 21A shows a cross section of an elongated speaker 301 disclosed in Japanese Patent No. 3956485, and FIG. 21B shows perspectively a relevant portion of the speaker 301. In FIG. 21A, the cross section of the speaker 201 taken along the minor axis direction is shown in the left side and the cross section thereof taken along the major axis direction is shown in the right side like in FIG. 20.
Referring to FIGS. 21A and 21B, in the speaker 301, a voice coil 302 is disposed and located outward of the inner circumference of a surround 303 at the minor axis direction area, and parts 305 of the front end portion of the voice coil 302 are cut off to prevent the voice coil 302 from making contact with the surround 303, which enables the diameter of the voice coil 302 to be successfully increased without decreasing the width of the surround 303 positioned at the minor axis direction area thereby ensuring the withstanding of high power input.
Another solution for the problem described above is proposed in Japanese Patent Application Laid-Open No. 2006-311156. FIG. 22 shows a cross section of a conventional speaker 401 disclosed in Japanese Patent Application Laid-Open No. 2006-311156. In the speaker 401 shown in FIG. 22, a voice coil bobbin 403 has a larger diameter than a diaphragm (center dome) 402, an extension member 404 is disposed between the voice coil bobbin 403 and the diaphragm 402, and an inner circumferential portion of a surround (peripheral dome) 405 is connected to the extension member 404.
In the speaker 401 of FIG. 22, with provision of the extension member 404, the width of the surround 405 does not have to be decreased even if the diameter of the voice coil bobbin 403 is increased, and so the withstanding of power input can be increased.
In the speaker 301 disclosed in Japanese Patent No. 3956485, however, the process of cutting off the parts 305 of the front end portion of the voice coil 302 is additionally required, and also the workability in assembling the speaker 301 is deteriorated because the voice coil 302 has to be set in place with respect to the circumferential direction because of the provision of the parts 305 cut off. These factors can lead to the increase of the component cost and the product cost.
Also, in the speaker 401 disclosed in Japanese Patent Application Laid-Open No. 2006-311156, the extension member 404 is a flat plate having in top plan view a substantially elongated ring shape corresponding to the voice coil bobbin 403 and therefore cannot be applied to an elongated speaker including a normal round voice coil. Further, the speaker 401 is a micro speaker with no spider and so is inferior in the reproductive performance in the lower frequency.